Coating compositions based on polyurethaneureas play a major role because of their excellent properties, for example high scratch resistance and cold flexibility. Because of rising environmental and other legal requirements, the solvent-free aqueous polyurethaneureas are of particular importance. Coatings based on polyurethaneurea dispersions are used in different applications, for example textile coating, painting of plastics and automobiles, and in the electronics sector.
The use of polyurethaneurea dispersions for production of glass fibre sizes is also known, for example, from DE 199 14 885 A1 or EP 2 209 828 A1. Such sizes essentially serve to prevent abrasion between glass fibres during the process of their manufacture. In addition, size-coated glass fibres also have improved strength and improved flow capacity. Thus, demands are made on the polyurethaneurea present in the dispersions in relation to good adhesion and interaction with the glass fibre.
If such glass fibres are used to reinforce plastics (fibre-reinforced composite materials), the size must additionally also assure good compatibility with the plastic (matrix plastic), in order to function as a mediating layer between the glass fibre and the matrix material. Good attachment both to the matrix material and the glass fibre leads to good mechanical properties in the sense of reinforcement of the matrix material (for example increasing the transverse tensile strength or compressive shear strength).
Many such matrix materials are based on epoxy resins. Therefore, more particularly, there are also known size formations based on aqueous epoxy resins, since it is assumed that these can ensure good compatibility between size and matrix material (see, for example, EP 0 293 647 A or EP 0 741 979 A). However, the use of epoxy resins for coating of fibres is not possible for all applications for health reasons, and it is not impossible that the fibres coated with epoxy resins are not storage-stable because of the high reactivity of the epoxy group. Therefore, there is a fundamental interest in alternative size formulations.
DE 199 14 885 A1 describes polyurethaneurea dispersions which have dimethylpyrazole-blocked isocyanate groups and can be used as size for glass fibres. Disadvantages of blocked aqueous polyurethaneurea dispersions are the fact that partial deblocking takes place in the course of the typically forced drying of the fibres, and that the blocking agent is generally in free form after the elimination, which can lead to deterioration (e.g. discolouration) in properties of the fibres.
EP 2 209 828 A1 discloses size compositions based on aqueous polyurethaneurea dispersions having specific formation components. However, optimization of the reinforcing properties is fundamentally desirable.